This invention relates to a method of testing optical fiber centering devices, and, in particular, to a method of testing the accuracy of construction of a molded, integral, transparent, telecentric optical fiber connector body. Accordingly, it is a general object of this invention to provide new and improved methods of such character.
As more fully set forth in our co-pending application Ser. No. 454,943, filed Jan. 3, 1983, there is described an optical fiber centering device for centering the principal axis of an optical fiber along a predetermined axis of the device and for positioning an end of the fiber to a specific location along the predetermined axis, such device including a receiving member and elastomeric insert means. The receiving member has a cylindrical cavity therewithin having an axis of revolution coincident with the predetermined axis. The cylindrical cavity terminates at an interior end surface. The interior end surface contains a truncated conical recess for further centering an end of the optical fiber along the predetermined axis to a degree greater than that achievable in the absence of the recess, such that the following occurs:
(a) All cross-sections through the recess and perpendicular to the predetermined axis are circular with their centers on the said axis; PA0 (b) The size of the cross-section of the recess at the interior end surface of the cylindrical cavity is greater than that of the largest diameter fiber to be centered and positioned; PA0 (c) The size of the cross-sections decreases smoothly and monotonically away from the cylindrical cavity end surface until the recess terminates at a cross-section smaller than that of the smallest diameter fiber to be centered and positioned such that an inserted fiber is guided smoothly along the wall of the recess and is stopped when the cross-sectional dimensions of the recess no longer is greater than the diameter of the inserted fiber; and PA0 (d) The depths of the cylindrical cavity and the recess are such that the specific location along the predetermined axis where the one end of the fiber is to be positioned is where the cross-sectional dimensions of the recess permits the nominal dimensions of the fiber to be centered and positioned. The elastomeric insert means is insertable to the cylindrical body, the insert means having an internal passageway. Thus, an optical fiber inserted into the elastomeric insert means causes resulting elastic restoring forces to automatically center the fiber along the predetermined axis.
As stated in that 1983 application, the depth of the truncated conical recess can be 0.015 inch, the recess can terminate at a cross-section of 0.003 inch, the wall of the recess can form an angle of 30.degree. with respect to the predetermined axis, the receiving member can be an integral part of a telecentric optical connector, and the telecentric optical connector can include an integrally molded lens surface whose optical axis coincides with the predetermined axis and whose focal point coincides with the specific location.
The telecentric optical fiber connector, wherein light from an optical fiber is emitted from the connector lens in a comparatively large diameter parallel beam, can be referred to as an expanded beam connector. It includes two primary components: One, an integral, optical quality, plastic connector body having an annular planar reference surface substantially perpendicular to an optical axis. A recessed convex lens surface is molded, inwardly from the reference surface. The body is substantially cylindrical, and is so configured to be engageable with a similar body. The opposite axial end of the body has a central cylindrical cavity therein which extends to a point which is one focal length from the lens surface, the truncated conical recess being located at such point. The second component, a fiber holder, holds an optical fiber centrally within the cavity, and abuts an end of the fiber against that point which is one focal length from the lens surface. Index-matching material can be applied to the end of the fiber.
The expanded beam connector (or receiving part) consists essentially of an integrally formed, fiber alignment part, a collimating lens, and a reference surface. Optimum performance is achieved by locating the fiber on the optical axis with submicron accuracy, thereby minimizing loss. The optical axis is an imaginary line normal to the reference surface drawn through the apex of the lens. The position of the fiber is defined by the conical recess and the fiber axis that coincides with the conical axis. A concern in the mass production by injection molding of such parts is the availability of a production method to measure the departure of the cone axis from the optical axis. A production measurement permits an immediate correction of any deviations, as well as determination of the correct parameters required for molding.
In the past, the development of an expanded beam connector was impeded by the lack of such measurement technique. The development of the expanded beam connector required the measurement of the angle that the collimated beam emerging from the lens makes with respect to the reference surface. Prior art techniques were generally destructive and resulted in long response time. The prior art techniques had their accuracy dependent upon fiber cleave angle, assembly procedure and fiber insertion techniques, thus being unsatisfactory for monitoring a production process. For quality control purposes, the prior art destructive techniques posed serious problems in terms of their suitability for large sampling ratios.